The present invention relates to precipitated silicic acids (silica), a process for their preparation, and their use in rubber mixtures.
It is known to incorporate precipitated silicas into rubber mixtures (see Wolff, Kautschuk, Gummi, Kunstst. 7 (1988) p.674). Precipitated silicas have to be readily dispersible when used in rubber mixtures. A poor dispersibility is often the reason why precipitated silicas are not used in tire mixtures.
Document WO 95/09128 discloses precipitated silicas that can be used in tires. Their use in tire carcasses is however not mentioned.
On account of the more stringent requirements of the tire industry, even the improved dispersion of this precipitated silicic acid is no longer sufficient for use in tire treads.
WO 96/30304 describes a precipitated silica that can be dispersed in tire treads.
Using the known precipitated silica described in WO 96/30304 it is possible to achieve a reduction in the rolling resistance of the tire by 20-30% compared to tires filled with carbon black. This corresponds to a saving in fuel of ca. 5%.
Different tire constituents contribute in various proportions to the rolling resistance of an automobile tire:
Tread: 50% Belt.: 20% Carcase: 10% Side wall: 10% Tire bead: 5% Inner layer: 5%
In a truck tire the proportion of the individual tire segments to the rolling resistance differs from the distribution in an automobile tire:
 Tread: 30% Belt: 20% Carcase: 24% Side wall: 10% Tire bead: 16%
This distribution of the proportions contributing to the rolling resistance shows that in automobile tires 50% and in truck tires even up to 70% of the rolling resistance is due to structural parts of the tire carcase. Up to now carbon black has overwhelmingly been used as active filler in tire carcasses.
Some sections of the automobile industry demand that the rolling resistance be reduced by approximately a further 10%. Up to now it has not been possible to achieve his.
An object of the present invention is to achieve a further considerable reduction in the rolling resistance of tires.
Another object of the invention is to achieve a precipitated silica that is easily dispersible in tire carcasses.
Truck tire customers are in addition asking for an increase in the service life of truck tires. Another object of the present invention is to meet this request, combined with a reduction in the amount of heat generated.